Une première partie de ce mémoire portera sur l’analyse des états fondamentaux ma- gnétiques de deux composés isolants et magnétiquement frustrés SrDy2O4 et SrHo2O4. Une étude de la chaleur spécifique à basse température sous l’effet de champs magné- tiques de ces échantillons a été menée afin de détecter la présence de transitions de phases. L’utilisation d’un composé isotructurel non magnétique, le SrLu2O4, a permis l’isolement de la composante magnétique à la chaleur spécifique. Les comportements observés sont non conformes avec les transitions magnétiques conventionnelles. De plus, le calcul de l’entropie magnétique ne montre qu’un recouvrement partiel de l’entropie associée à un système d’ions magnétiques. En second lieu, une analyse des oscillations quantiques de Haas-van Alphen a été effectuée dans le LuCoIn5, composé apparenté au supraconducteur à fermions lourds CeCoIn5. Les résultats obtenus montrent une topologie de la surface de Fermi très différente comparativement aux CeCoIn5 et LaCoIn5, ayant un comportement beaucoup plus tridimensionnel sans les cylindres caractéristiques présents chez les autres membres de cette famille. Finalement, le montage d’un système de détection PIXE a permis l’analyse nucléaire d’échantillons afin de déterminer la concentration de chacun des éléments les constituant. L’analyse a été effectuée sur une série d’échantillons YbxCe1−xCoIn5 dont le changement de concentration a des effets importants sur les propriétés du système. / The first part of this thesis consist of the analysis the magnetic ground states of two magnetically frustrated insulator compounds SrDy2O4 and SrHo2O4. A study of the low temperature specific heat in magnetic fields has been carried on in order to detect phase transitions. The magnetic contribution to the specific heat has been determined using the isostructural but non magnetic compound SrLu2O4. The observed behaviour does not conform with conventional magnetic phase transitions. Also, the calculated magnetic entropy shows only a partial recovery of the entropy normally associated with magnetic ions in the systems. In the second study, I measured and analyzed de Haas-van Alphen quantum oscil- lations in LuCoIn5, a compound related to the heavy fermion superconductor CeCoIn5. The obtained results show a Fermi surface topology greatly differing from the CeCoIn5 and LaCoIn5, having a much more tridimensional behaviour, compared to the characteristics cylinder exhibited by the other members of this family. In the last part of my thesis, I’m am describing the set up of a PIXE detection system used for the nuclear analysis of thick samples in order to calculate the concentra- tion of each element present. The analysis has been carried on a series of samples of YbxCe1−xCoIn5, where the variation of concentration has major repercussions on the electronic and magnetic properties of the system.

No description available.

Le but de ce travail est d’étudier la faisabilité de la détection de mouvements dans des séquences d’images en utilisant l’équation de continuité et la dynamique de supraconductivité. Notre approche peut être motivée par le fait que l’équation de continuité apparait dans plusieurs techniques qui estiment le flot optique. Un grand nombre de techniques qui utilisent les flots optiques utilisent une contrainte appelée contrainte de l’invariance lumineuse. La dynamique de supraconductivité nous permet de nous affranchir de la contrainte de l’invariance lumineuse. Les expériences se feront avec la base de données de séquences d’images CDNET 2014. Pour obtenir les résultats numériques en terme de score F1, une combinaison sera faite par la suite entre la dynamique de supraconductivité et un méchanisme d’attention qui est un résumé des vérites de terrain. / The goal of this work is to study the feasibility of motion detection in images sequences by using the continuity equation and superconductivity dynamics. Our approach can be motivated by the fact that many techniques that compute the optic flow use the continuity equation combined with a constraint that is called the brightness constancy constraint. The dynamics of superconductivity allows us to escape from the brightness consistency constraint. The experiments will be done with a database of images sequences named CDNET 2014. To obtain the numerical results in terms of F1 score a combination will be done between the dynamics of superconductivity and a mechanism of attention which is a resume of the ground truth.

L'état supraconducteur étant un condensat de paires de Cooper constitué d'électrons de moments et de spins opposés, il peut être fortement influencé par des effets de spin. Au cours de cette thèse, nous étudions l'effet d'un fort champ d'échange et d'un effet spin-orbite de type Rashba sur les propriétés supraconductrices. Dans une première partie, on étudie les effets associés à l'interaction entre supraconductivité et fort champ d'échange, se caractérisant par une transition de phase vers un état supraconducteur inhomogène découvert par Fulde, Ferrell, Larkin et Ovchinnikov (FFLO). On étudie tout particulièrement les fluctuations supraconductrices à l'approche de la transition de phase. On montre que ces fluctuations peuvent servir de révélateur à cette phase. Notamment, la capacité calorifique et la paraconductivité divergent de façon caractéristique à la transition vers un état modulé. On décrit également comment les effets paramagnétiques modifient les fluctuations de l'aimantation, annulant la réponse diamagnétique ou produisant des oscillations entre réponse para- et dia-magnétique. La seconde partie est dévolue aux jonctions supraconducteur-ferromagnétique (S/F). Dans les jonctions Josephson S/F/S, le champ d'échange donne lieu à des oscillations du courant critique en fonction de la longueur de la jonction, charactérisées par une alternance des états 0 et . On prédit une transition entre les états 0 et induite par la température, même dans la limite ballistique. Dans cette limite ballistique, on montre également que le courant de Josephson s'atténu sous la forme de lois de puissance en fonction de la longueur de la jonction, alors que le cas diffusif présente une atténuation exponentielle. On étudie ensuite la seconde harmonique de la relation courant-phase en présence d'une faible quantité d'impuretés. La dernière partie traite des effets de proximité lorsque les deux effets paramagnétique et spin-orbite sont présents dans une jonction Josephson. On montre que l'association d'une interaction Rashba et d'un champ d'échange induit un couplage direct entre les ordres magnétique et supraconducteur. En particulier, ce couplage permet de générer toute la dynamique magnétique par l'application d'une simple tension électrique. / The superconducting state being a Cooper pair condensate built on opposite spin and momentum electrons, it can be strongly influenced by any spin effect. In this thesis, we investigate the roles of strong paramagnetic and spin-orbit effects on superconducting properties. In a first part, the interplay between paramagnetic effect and bulk superconductivity is studied, leading to the modulated Fulde, Ferrell, Larkin and Ovchinnikov phase (FFLO phase). We focus on superconducting fluctuations near to the FFLO state. We show that these fluctuations can serve as a smoking gun for this phase. Noticeably, the fluctuation heat capacity and paraconductivity diverge in a characteristic way when approaching the phase transition towards a modulated state. Moreover, the fluctuation induced magnetization is predicted to be drastically quenched or to oscillate between dia- and para-magnetic responses. The second part is devoted to superconductor-ferromagnetic (S/F) junctions. In S/F/S Josephson junctions, the exchange field is responsible for the critical current oscillation, characterized by alternative 0- and -states, with respect to the junction length. We predict a temperature induced (0-) state transition, even in the ballistic case. Moreover, the ballistic case exhibits some power law decays of the Josephson current, in contrast to the exponentially decaying current in dirty limit. The moderately dirty limit is then investigated, and the second harmonic of the current-phase relation is established. The last part deals with proximity effects when both paramagnetic and spin-orbit interactions are present in a Josephson junction. We show that the association of both Rashba interaction and exchange field induces a direct coupling between magnetic and superconducting orders. Particularly, this coupling generates the complete magnetization dynamics by applying an appropriate d.c. voltage.

Le sujet de cette thèse est l'analyse du second champ critique supraconducteur (Hc2) ainsi que l'interaction entre la supraconductivité et les points critiques quantiques (PCQ), pour les composés CeCoIn5, URhGe et UCoGe. Dans le composé CeCoIn5, l'étude par résistivité du domaine de liquide de Fermi a permis la localisation précise du PCQ a pression ambiante. Cette analyse permet d'invalider l'hypothèse d'une coïncidence entre Hc2(0) et le PCQ. Dans une deuxième partie, l'évolution sous pression de Hc2 est analysée. Le dôme supraconducteur de ce composé est non-conventionnel avec deux pressions caractéristiques différentes: à ~1.6GPa, la température de transition supraconductrice est maximum alors que c'est à ~0.4GPa que la plupart des grandeurs physiques (maximum de Hc2(0), maximum de la pente dHc2/dT, maximum du saut de chaleur spécifique DC/C, ...) suggèrent la présence d'un PCQ. Nous expliquons cet antagonisme par l'importance des processus de brisure de pairs liés a la proximité du PCQ. Ces deux observations nous permettent de proposer un nouveau diagramme de phase pour CeCoIn5. Dans une troisième partie, les mesures de conduction thermique sur les composés URhGe et UCoGe sont présentées. Elles nous permettent dans un premier temps d'obtenir la transition "bulk" supraconductrice et de confirmer la forme in-habituelle de Hc2 observée en résistivité. La dépendance en températures et en champs de la conduction thermique nous permet d'identifier une contribution non-électronique au transport de chaleur jusqu'aux plus basses températures. D'autre part, nous identifions deux différents domaines supraconducteurs a bas et hauts champs appliqués selon l'axe b. Ces deux domaines sont compatibles avec un modèle de supraconductivité multigaps. Suivant ces observations et des mesures de pouvoir thermoélectrique, nous proposons un modèle de transition de Lifshitz pour ces deux composés. / The subject of this thesis is the analyze of the superconducting upper critical field (Hc2) and the interaction between superconductivity and quantum critical points (QCP), for the compounds CeCoIn5, URhGe and UCoGe. In CeCoIn5, study by mean of resistivity of the Fermi liquid domain allows us to localize precisely the QCP at ambient pressure. This analyze rule out the previously suggested pinning of Hc2(0) at the QCP. In a second part, the evolution of Hc2 under pressure is analyzed. The superconducting dome is unconventional in this compound with two characteristic pressures: at 1.6GPa, the superconducting transition temperature is maximum but it is at 0.4GPa that physical properties (maximum of Hc2(0), maximum of the initial slope dHc2/dT, maximum of the specific heat jump DC/C,... ) suggest a QCP. We explain this antagonism with pair-breaking effects in the proximity of the QCP. With these two experiments, we suggest a new phase diagram for CeCoIn5. In a third part, measurements of thermal conductivity on URhGe and UCoGe are presented. We obtained the bulk superconducting phase transition and confirmed the unusual curvature of the slope dHc2/dT observed by resistivity. The temperatures and fields dependence of thermal conductivity allow us to identify a non-electronic contribution for heat transport down to the lowest temperature (50mK) and probably associated with magnon or longitudinal fluctuations. We also identified two different domains in the superconducting region, These domains are compatible with a two bands model for superconductivity. Thermopower measurements on UCoGe reveal a strong anisotropy to current direction and several anomaly under field applied in the b direction. We suggest a Lifshitz transition to explain our observations in these two compounds.

Este trabalho tem como objetivo o estudo da influência do boro na fase αNb5Si3 (Fase T2) a baixas temperaturas analisando suas propriedades elétricas e magnéticas. Para o estudo deste tema as amostras foram preparadas, seguindo a estequiometria Nb5Si3-xBx, via metalurgia do pó e também por fusão a arco, com x dentro do intervalo limitado por 0  X  1,0. Estas amostras foram analisadas através de difratometria de raios x, microscopia eletrônica de varredura, magnetização, transporte elétrico e medidas calorimétricas em baixa temperatura. As medidas das propriedades elétricas e magnéticas destas fases mostram que a substituição de boro por silício induz supercondutividade na fase T2. O caráter volumétrico da transição supercondutora é confirmado pela medida de capacidade calorífica. Assim, este trabalho é o primeiro a mostrar uma nova família de materiais supercondutores que cristalizam na estrutura protótipo Cr5B3. / This work to study the influence of boron during low temperature αNb5Si3 (T2 phase) analyzing their electrical and magnetic properties. For the study of this subject the samples were prepared, following the stoichiometry Nb5Si3-xBx via powder metallurgy and also by arc melting process, with x within the range limited by 0X1.0. These samples were analyzed by X-ray diffraction, scanning electron microscopy, magnetization, electrical transport and calorimetric measurements of low temperature. Measurements of electrical and magnetic properties of these phases show that the substitution of boron by silicon induces superconductivity at the T2 phase. The bulk nature of superconducting transition is confirmed by heat capacity measurement. This study is the first to show a new family of superconducting materials that crystallize in the Cr5B3 prototype structure.

O presente trabalho analisou as condições de texturização de amostras de Ag/Bi2212 (Bi2Sr2CaCu2O8+δ) na forma de pastilhas e de fitas, verificando-se a influência do tratamento térmico, atmosfera, adição de prata e adição de zircônia ou zirconato de cálcio. As adições de zircônia ou de zirconato de cálcio, com partículas de dimensões submicrométricas ou nanométricas (abaixo de 200nm), foram analisadas como possíveis geradores de centros de aprisionamento de fluxo magnético, assim como foi feita a análise de seus comportamentos nas propriedades intrínsecas da matriz supercondutora. A influência da atmosfera de tratamento térmico foi analisada de modo a alterar a concentração de oxigênio na fase supercondutora visando melhores resultados de temperatura crítica, sem depreciação das densidades de corrente crítica e dos campos de irreversibilidade, Birr. Foram analisadas as influências dos parâmetros de tratamento térmico, tais como temperatura máxima de reação, tempo nesta temperatura máxima, taxa de resfriamento do estado líquido ao estado sólido, e temperatura e tempo de recozimento após solidificação. Verificou-se a influência do resfriamento do forno sobre a texturização e a temperatura crítica. Quanto à dopagem com prata, foi verificada sua influência na texturização e interação com a zircônia. Foram realizadas caracterizações supercondutoras e microestruturais das amostras. / The present work analyzed the texturing conditions of Ag/Bi2212 samples (Bi2Sr2CaCu2O8+δ) in the form of bulks and of tapes, verifying the influence of heat treatment, atmosphere, silver addition and addition of zirconia or calcium zirconate. The additions of zirconia or calcium zirconate, with particles of submicron or nanometric (below 200nm) dimensions, were analyzed as possible generators of magnetic flux pinning centers, as well as it was analyzed their behaviors on the intrinsic properties of the superconducting matrix. The influence of the heat treatment atmosphere was analyzed in order to change the oxygen concentration in the superconducting phase aiming better results of critical temperature, without depreciation of the critical current densities and of the irreversibility fields, Birr. The influences of the heat treatment parameters were analyzed, such as the reaction maximum temperature, soaking time at this maximum temperature, cooling rate from the liquid to the solid states, and annealing temperature and time after solidification. It was verified the influence of the furnace cooling rate on the texturing and critical temperatures. Concerning to the silver addition, it was verified its influence on the texturing and its interaction with the zirconia. Superconducting and microstructural characterizations of the samples were performed.

Made available in DSpace on 2017-07-21T19:25:56Z (GMT). No. of bitstreams: 1 pauladeazambuja.pdf: 3846623 bytes, checksum: 775b83dd168b0a44745812c2ca7a454a (MD5) Previous issue date: 2008-03-28 / Fundação Araucária de Apoio ao Desenvolvimento Científico e Tecnológico do Paraná / In this work is presented an experimental study on the effects of the addition of Ag to the system YBa2Cu3O7-d. The silver can be added to the YBa2Cu3O7-d system through the mixture with metallic Ag, with oxide of silver (Ag2O) or with nitrate of silver (AgNO3), using different techniques and forms of processing. The addition of silver to the YBa2Cu3O7-d system is known by minimizing the properties undesirable of the system, without deleterious effects in superconducting properties. She is responsible for the significant increase in the conductivity thermal and electric of the system; it improves of the mechanical properties, as the resistance of fracture and elasticity of the material, from the reduction of the porosity; it reduces the weak links between the superconducting grains, improving the contact between the same. The samples used in this work had been processed for different experimental routes: in the first set of samples Ag2O was added to the YBa2Cu3O7-d system previously prepared; on the second set of samples the silver oxide was mixed to the precursors Y2O3, BaCO3 and CuO and then the YBa2Cu3O7-d system was processed; and in the third set of samples metallic silver was added to the YBa2Cu3O7-d system previously prepared. The characterization of the samples, pure and doped with silver, was realized through with aid of different techniques enclosing: analysis of the crystalline structure; analysis of the superficial topology; measures calorimetric; mechanical properties; properties of electronic transport and magnetic properties. The obtained results are coherent with results of other works on composites YBa2Cu3O7-d/Ag and demonstrate that the addition of the silver to the YBa2Cu3O7-d system, of a general form, improves the properties of this system. Key Words: Superconductivity; YBa2Cu3O7-d system; processing of composites YBa2Cu3O7-d/ Ag; characterization of materials. / Neste trabalho é apresentado um estudo experimental sobre os efeitos da adição de Ag ao sistema YBa2Cu3O7-d. A prata pode ser adicionada ao sistema YBa2Cu3O7-d através da mistura com Ag metálica, com óxido de prata (Ag2O) ou com nitrato de prata (AgNO3), utilizando diferentes técnicas e formas de processamento. A adição de prata ao sistema YBa2Cu3O7-d é conhecida por minimizar as propriedades indesejáveis do sistema, sem deteriorar as propriedades supercondutoras. Ela é responsável pelo aumento significativo nas condutividades térmica e elétrica do sistema; melhora das propriedades mecânicas, como a resistência à fratura e elasticidade do material, a partir da redução da porosidade; reduz as ligações fracas entre os grãos supercondutores, melhorando o contato entre os mesmos. As amostras utilizadas neste trabalho foram processadas por rotas experimentais diferentes: no primeiro lote de amostras foi adicionado Ag2O ao sistema YBa2Cu3O7-d previamente preparado; no segundo lote de amostras o óxido de prata foi misturado aos precursores Y2O3, BaCO3 e CuO e então o sistema YBa2Cu3O7-d foi processado; e no terceiro lote de amostras prata metálica foi adicionada ao sistema YBa2Cu3O7-d previamente preparado. A caracterização das amostras, pura e dopada com prata, foi realizada com auxílio de diferentes técnicas abrangendo: análise da estrutura cristalina; análise da topologia superficial; medidas de calorimetria; propriedades mecânicas; propriedades de transporte eletrônico e propriedades magnéticas. Os resultados obtidos são coerentes com resultados de outros trabalhos sobre compósitos YBa2Cu3O7-d/Ag e demonstram que a adição da prata ao sistema YBa2Cu3O7-d , de uma forma geral, melhora as propriedades deste sistema.

Made available in DSpace on 2017-07-21T19:26:07Z (GMT). No. of bitstreams: 1 Simoneapa.pdf: 1470043 bytes, checksum: b380a790ad5236069470caa27e038eed (MD5) Previous issue date: 2007-03-02 / In this work, it was accomplished an experimental study about the substitution of the yttrium atom (Y) in the YBa2Cu3O7-x superconductor system for a rare earth oxide (RE2O3), gotten from the xenotime ore. Chemically, this substitution is possible due to the equality of the oxidation state between the Y3+ ions and the earth rare ions, which form the oxide. This way, this substitution should not modify the properties of the superconductor system significantly. The xenotime in its natural form is composed of a rare earth phosphate, zirconita and other heavy elements. The zirconita and the heavy elements can be separated by magnet or gravimetric process. The rare earth phosphate is chemically treated by the acid or the alkaline leaching process, resulting in a rare earth oxide (RE2O3). The xenotime ore used in this work was extracted from the Pitinga mine (AM, Brazil). Four polycrystalline samples were processed through the solid-state reaction, from the precursors: rare earth oxide (RE2O3), barium carbonate (BaCO3) and copper oxide (CuO), forming the REBa2Cu3O7-x superconducting oxide. The chracterization of the samples crystalline structures was studied by x-ray diffraction. The analysis of the samples superficial morphology was studied by optical microscopy and scanning electron microscopy (SEM). The properties of electronic transportation were analyzed by measurements of electric resistivity. Among the analyzed samples, one did not present null state of electric resistance. The measurements of electric resistivity for the other samples revealed superconductor behavior and showed that the critical temperature of the REBa2Cu3O7-x system is around 90 K, as in the YBa2Cu3O7-x system. Such values were confirmed by the measurement of magnetic susceptibility. The analyses of the Xray diffractograms of the samples revealed that the cell parameters of both systems are equal. These results indicate that the substitution of the Y for the rare earth oxide is possible, which may have important implications both from the point of view of basic research and the applied research. / Neste trabalho foi realizado um estudo experimental da substituição do átomo de ítrio (Y) no sistema supercondutor YBa2Cu3O7-x, por um óxido de terras-raras (RE2O3), obtido a partir do minério xenotima. Quimicamente essa substituição é possível devido à igualdade do estado de oxidação entre os íons Y3+ e os íons de terras-raras que formam o óxido. Dessa forma, essa substituição não deve alterar de forma significativa as propriedades supercondutoras do sistema. A xenotima em sua forma natural é constituída por um fosfato de terras-raras, zirconita e outros elementos pesados. A zirconita e os elementos pesados podem ser separados por processos magnéticos ou gravimétricos. O fosfato de terras-raras é tratado quimicamente pelo processo de lixiviação ácida ou alcalina, resultando em um óxido de terras-raras (RE2O3). O minério xenotima utilizado neste trabalho foi extraído da mina do Pitinga (AM, Brasil). Foram processadas quatro amostras policristalinas através da reação de estado sólido, a partir dos precursores: óxido de terras raras (RE2O3), carbonato de bário (BaCO3) e óxido de cobre (CuO), formando o óxido supercondutor REBa2Cu3O7-x. A caracterização das estruturas cristalinas das amostras foi estudada por difração de raios X. A análise da morfologia superficial das amostras foram estudadas por microscopia óptica e microscopia eletrônica de varredura (MEV). As propriedades de transporte eletrônico foram analisadas através de medidas de resistividade elétrica. Das amostras processadas, uma não apresentou estado de resistência elétrica nula. As medidas de resistividade elétrica para as demais amostras revelaram comportamento supercondutor e mostraram que a temperatura crítica do sistema REBa2Cu3O7-x, está em torno de 90 K, como no sistema YBa2Cu3O7-x. Esses valores foram confirmados pelas medidas de susceptibilidade magnética. As análises dos difratogramas de raios X das amostras revelaram que os parâmetros de cela dos dois sistemas são iguais. Esses resultados indicam que substituição do Y pelo óxido de terras-raras é possível, podendo ter importantes implicações tanto do ponto de vista de pesquisa básica como da pesquisa aplicada.

Made available in DSpace on 2017-07-21T19:26:09Z (GMT). No. of bitstreams: 1 Thiago Luis Schneider.pdf: 9685610 bytes, checksum: 1d228206aa0873ceb2084087b0fc033f (MD5) Previous issue date: 2014-03-28 / Abstract Abstract / Resumo Resumo